Effect Of UV₂₅₄ Disinfection And Potassium Permanganate On The Photochemical Reactivity Of Dissolved Organic Matter

Dissolved organic matter（DOM）is almost ubiquitous in aquatic environments.DOM produces reactive substances such as triplet states of DOM（³DOM^*）,singlet oxygen（¹O₂）and hydroxyl radical（^·OH）under sunlight irradiation,which play an important role in the transport and transformation of trace pollutants in water.UV₂₅₄disinfection and potassium permanganate oxidation are common processes in water treatment.The structural composition,molecular weight,functional groups and other physicochemical property of DOM will be changed after UV₂₅₄disinfection and potassium permanganate oxidation,which can affect the photoformation of reactive substances from DOM.However,the mechanisms of these two water treatment processes on the photoreactivity of DOM are still unclear.In this study,the effluent organic matter（Ef OM）,typical humic substances（HS）and natural organic matter（NOM）were selected as research objectives,exclusion chromatography（SEC）,ultraviolet-visible spectroscopy（UV-Vis）and fluorescence spectroscopy（3DEEM）were applied to characterize the change of physicochemical properties of DOM after UV₂₅₄disinfection and potassium permanganate oxidation,probe compounds were applied to measure the generation of reactive substances from DOM,and the correlation between physicochemical property and photochemical activity of DOM was also analyzed.The main contents and conclusions of the experiment are as follows:Effect of UV₂₅₄disinfection on the photochemical reactivity of DOM:（1）The aromaticity,fluorescence intensity and molecular weight of Ef OM and HS decreased after disinfection by UV₂₅₄.（2）Under simulated sunlight irradiation,the formation rate of³DOM^*decreased,the formation rate and steady state concentration of ¹O₂decreased while the formation rate and steady state concentration of^·OH increased after UV₂₅₄disinfection.（3）After UV₂₅₄disinfection,the triplet quantum yield coefficient of ³DOM^*(f _TMP)and the quantum yield of¹O2(Φ_1O2)in Ef OM samples increased,f _TMPandΦ_1O2in HS samples decreased,and the quantum yield of^·OH(Φ·_OH)in Ef OM and HS both increased.The relationship between f _TMPand Φ_1O2was positive linear for Ef OM and HS samples,the relationship between f _TMPandΦ·_OHwas positive linear for Ef OM samples while there were negative linear correlations for HS samples.（4）Before UV₂₅₄disinfection,f _TMP,Φ_1O2andΦ·_OHwere positively liner correlated to E2/E3（absorbance ratio of 254 nm and 365 nm）.After UV₂₅₄disinfection,the relationship betweenΦ·_OHand E2/E3 was positively linear for Ef OM and HS samples,f _TMPandΦ_1O2of Ef OM samples were both positively linear correlated to E2/E3 while f _TMPandΦ_1O2of HS samples were both negatively linear correlated to E2/E3.Effect of potassium permanganate oxidation on the photochemical reactivity of DOM:（1）The aromaticity,fluorescence intensity and molecular weight of NOM decreased after potassium permanganate oxidation.（2）Under simulated sunlight irradiation,the formation rate of ³NOM^*increased while the formation rate and steady state concentration of ¹O₂and^·OH decreased after permanganate oxidation.（3）After potassium permanganate oxidation,f _TMPandΦ_1O2increased whileΦ·_OHdecreased in all NOM samples.The relationship betweenΦ_1O2and f _TMPwas positively linear,and the relationship betweenΦ·_OHand f _TMPwas negative linear.（4）f _TMPandΦ_1O2were both positively linear correlated to E2/E3 before and after oxidation with potassium permanganate.